Electric motor and heat sink apparatus using the same

ABSTRACT

An electric motor includes a frame including a cylindrical frame housing having an open end, a sleeve fitted in the frame housing, a stator attached to the outer peripheral part of the frame housing, and a rotor including a magnet disposed opposite to the stator and rotating shaft 9 rotatably and pivotally supported by the sleeve and having one fixed end. At a center portion of rotating shaft 9, tapered part 9d whose diameter decreases toward front end part 9a side is formed. Oil is provided to a gap between rotating shaft 9 and the sleeve.

CROSS REFERENCE TO RELATED APPLICATIONS

Japanese Patent Applications No. 2017-118866 filed on Jun. 16, 2017, No.2017-150661 filed on Aug. 3, 2017 and No. 2017-234241 filed on Dec. 6,2017, including description, claims, drawings, and abstract the entiredisclosure is incorporated herein by reference in its entirety.

TECHNOLOGICAL FIELD

The present invention relates to an electric motor and a heat sinkapparatus using the same.

BACKGROUND ART

In an electronic apparatus, a heat sink apparatus is mounted for thepurpose of cooling. The heat sink apparatus generates air flow byrotating a fan with an electric motor so as to remove heat from a heatgeneration member.

PTL 1 discloses an electric motor (spindle motor) intended to achievedownsizing, impact resistance, low noise, and low power consumption.

CITATION LIST Patent Literature

PTL 1

Japanese Patent Application Laid-Open No. H6-269142

SUMMARY OF INVENTION Technical Problem

In recent years, heat sink apparatuses have been used in varioustechnical fields including the field of medical equipment, and the lifetime of the heat sink apparatuses is desired to be increased.

Embodiments of the present disclosure disclose an electric motor and aheat sink apparatus using the same which can achieve longer life time incomparison with a conventional art.

Solution to Problem

An electric motor according to a mode of the present disclosureincludes: a frame including a frame housing having a cylindrical shapewhose one end is open; a sleeve fitted in the frame housing; a statorattached to an outer peripheral part of the frame housing; and a rotorincluding a rotating shaft rotatably and pivotally supported by thesleeve, and a magnet that is disposed opposite to the stator, one end ofthe rotating shaft being fixed. The rotating shaft has a columnar shape.A tapered part having a tapered shape whose diameter decreases toward aside of a front end of the rotating shaft is formed in a center portionof the rotating shaft, the front end being a free end. A length of thetapered part is greater than a diameter of the rotating shaft. Oil isprovided to a gap between the rotating shaft and the sleeve.

Advantageous Effects of Invention

According to the present disclosure, it is possible to achieve longerlife time in comparison with a conventional art.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view of an electric motor in a heat sink apparatusaccording to Embodiment 1 of the present disclosure;

FIGS. 2A to 2E illustrate external shapes of a rotating shaft of theelectric motor according to Embodiment 1 of the present disclosure;

FIG. 3 is a sectional view of an electric motor in a heat sink apparatusaccording to Embodiment 2 of the present disclosure;

FIG. 4 illustrates an external shape of a sleeve of the electric motoraccording to Embodiment 2 of the present disclosure;

FIG. 5 is a sectional view of an electric motor in a heat sink apparatusaccording to Embodiment 3 of the present disclosure;

FIGS. 6A to 6F illustrate external shapes of a rotating shaft of theelectric motor according to Embodiment 3 of the present disclosure;

FIG. 7 shows evaluations for each of ratios between tapered parts in therotating shaft of the electric motor according to Embodiment 3 of thepresent disclosure;

FIG. 8 is a sectional view of an electric motor in a heat sink apparatusaccording to Embodiment 4 of the present disclosure;

FIGS. 9A to 9F illustrate external shapes of a sleeve of the electricmotor according to Embodiment 4 of the present disclosure; and

FIG. 10 shows evaluations for each of ratios between tapered parts inthe sleeve of the electric motor according to Embodiment 4 of thepresent disclosure.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present disclosure are described in detail below withreference to the accompanying drawings. It should be noted that detailsmay be omitted in the descriptions as necessary. For example, details ofwell-known matters, overlapping descriptions between substantiallyidentical configurations and the like may be omitted to avoidunnecessary redundancy in the descriptions, and to facilitateunderstanding of a person skilled in the art.

The advantages and features provided by the embodiments of the inventionwill become more fully understood from the detailed description givenhereinbelow and the appended drawings which are given by way ofillustration only, and thus are not intended as a definition of thelimits of the present invention.

Embodiment 1 Configuration of Electric Motor

FIG. 1 is a sectional view of an electric motor in a heat sink apparatusof Embodiment 1. Cylindrical frame housing 1 a having an open end ismounted in frame 1. Substrate 4 and stator 3 of the electric motor areattached to an outer peripheral part of frame housing 1 a. Stator 3 iscomposed of insulation part 14 formed of an insulating material such asa synthetic resin, iron core 15 that is a stack of a plurality of thinplates, and coil 16 wound around iron core 15.

In the side wall of frame 1, a predetermined number of openings of apredetermined size through which air flow passes (not illustrated) areprovided toward a predetermined direction. In addition, the bottom partof frame 1 on the side on which frame housing 1 a is not providedincludes a plane area where a heat generation member such as asemiconductor device can be attached. In addition, thrustor 5 formed ofa resin is fixed on the bottom surface.

In frame housing 1 a, sleeve 6 is fitted, and fixation ring 7 thatpresses down sleeve 6 is inserted. The end portion of fixation ring 7 onthe insertion side is tilted inward at, for example, approximately 10degrees so that it can be readily press-fitted into frame housing 1 a.

Fan 8 is composed of a blade (not illustrated) and rotor main body 10 ofthe electric motor. Rear end part 9 b of rotating shaft 9 is insertedand fixed at a center of rotor main body 10. In addition, magnet 11 andmagnet yoke 12 are fixed to rotor main body 10 by bonding or the like soas to face annular stator 3. The rotor of the electric motor is composedof rotating shaft 9, rotor main body 10, magnet 11 and magnet yoke 12.

Further, in rotor main body 10, recessed oil pool 10 a for reducingintrusion of external foreign matters and dusts into the bearing isformed at a portion around rotating shaft 9. In addition, in rotor mainbody 10, rib 10 b is formed at the outer periphery of oil pool 10 a andon the inner side of fixation ring 7.

Rotating shaft 9 is rotatably and pivotally supported by sleeve 6. Adynamic-pressure generation groove (not illustrated) for facilitatingthe rotation of rotating shaft 9 is formed by ball rolling or the likeon the inner peripheral surface of sleeve 6. Oil 13 is provided aslubricating oil to the dynamic-pressure generation groove, and thus aradial bearing with a bearing gap of 2 to 12 μm on each side fromrotating shaft 9 is formed.

It is to be noted that the dynamic-pressure generation groove may beformed on the outer peripheral surface of first straight part 9 e and/orsecond straight part 9 f of rotating shaft 9 (see FIGS. 2A to 2E).

Front end part 9 a (the free end opposite to rear end part 9 b) ofrotating shaft 9 is finished in the form of a spherical surface, andforms a thrust bearing in contact with thrustor 5.

Between frame housing 1 a and sleeve 6, ventilation groove 1 b thatextends from the opening to the bottom surface of frame housing 1 a isformed at the inner wall of frame housing 1 a. In addition, oil pool 6 athat is a circumferential groove is formed on the front end side (theside close to the bottom surface of frame housing 1 a) of the outerperipheral surface of sleeve 6.

With the electric motor having the above-mentioned configuration, asurplus of oil 13 in the bearing can be stored in oil pool 6 a on theouter periphery of the sleeve through ventilation groove 1 b, and it isthus possible to increase the acceptable variation and the supply amountof oil.

It is to be noted that a copper alloy such as C3604 and BC6C is used asthe material of sleeve 6 in consideration of the cutting performanceand/or the rolling performance, and a stainless steel such as SUS420J2is used as the material of rotating shaft 9 in consideration of the wearresistance and/or the handleability. In addition, fluorinated syntheticoil is used as oil 13 in view of ensuring high temperature heatresistance, and an additive is added thereto in order to slightlyimprove the extreme pressure performance.

In the heat sink apparatus of the present embodiment, when the rotor ofthe electric motor is rotated, fan 8 (blade) is also rotated, and air issucked along the axis direction of rotating shaft 9 of the electricmotor. The sucked air is exhausted from the opening provided in the sidewall of frame 1. At this time, the air flow removes the heat of frame 1transferred from the heat generation member. In this manner, the heatgeneration member is cooled.

Shape and Dimension of Rotating Shaft 9

Now the shape and the dimension of rotating shaft 9 of the presentembodiment are described with reference to FIGS. 2A to 2E. It is to benoted that the examples of rotating shaft 9 illustrated in FIGS. 2A to2E are different in their taper angles.

Rotating shaft 9 has a straight columnar shape whose diameter isconstant. Front end part 9 a of the free end of rotating shaft 9 isfinished in the form of a spherical surface. Knurling for attaching torotor main body 10 is provided on rear end part 9 b of rotating shaft 9.

In addition, tapered part 9 d having a tapered shape whose diameterdecreases toward front end part 9 a side is formed at a center portion(a portion where no dynamic pressure is generated) of rotating shaft 9.With this configuration, base part 9 c (a portion other than front endpart 9 a and rear end part 9 b) of rotating shaft 9 is sectioned intotapered part 9 d, first straight part 9 e on front end part 9 a side,and second straight part 9 f on rear end part 9 b side. It is to benoted that constriction part 9 g is formed at the connecting portionbetween tapered part 9 d and first straight part 9 e. In addition,constriction part 9 h is formed at the connecting portion between rearend part 9 b and second straight part 9 f.

Dynamic-pressure generation grooves may be formed on the outerperipheral surfaces of first straight part 9 e and second straight part9 f.

Rotating shaft 9 has a total length of 9 mm and an outer diameter of 1.2mm, for example. In addition, first straight part 9 e has a length of1.4 mm, tapered part 9 d including constriction part 9 g has a length of2.2 mm, and second straight part 9 f has a length of 2.9 mm, forexample.

Effect

As described above, in the present embodiment, tapered part 9 d isformed at a center portion of rotating shaft 9 of the electric motor.With this configuration, by a capillary force, oil 13 can be intimatelyapplied to a part (second straight part 90 of rotating shaft 9 on rotormain body 10 side, and it is thus possible to achieve longer life timein comparison with a conventional art.

To prove the above-mentioned effects, the present inventors conducteddurability tests with rotating shaft 9 provided with tapered part 9 dillustrated in FIGS. 2A to 2E and a rotating shaft provided with a stepin which a recessed groove (having a depth of approximately 0.1 mm) isformed in place of tapered part 9 d.

The tests were conducted under the same condition. In the conditionwhere the outside air temperature was 120° C., the lifetime of theapparatus using the rotating shaft provided with a step wasapproximately 1,200 hours, whereas the lifetime of the apparatus usingrotating shaft 9 provided with tapered part 9 d was approximately 2,200hours. In addition, in the condition where the outside air temperaturewas 100° C., the lifetime of the apparatus using the rotating shaftprovided with a step was approximately 2,000 hours, whereas no defectwas caused in the apparatus using rotating shaft 9 provided with taperedpart 9 d even after the apparatus was operated for 8,000 hours or more.

In addition, as a result of a study on the capillary force, it wasconfirmed that the desirable taper angle of tapered part 9 d is 1 to 3degrees (FIGS. 2A to 2C).

In addition, it was confirmed that a similar effect is achieved also inthe case where a step part provided with multi steps whose diametersdecrease toward front end part 9 a side is formed in place of taperedpart 9 d at a center portion (a portion where no dynamic pressure isgenerated) of rotating shaft 9.

It is to be noted that, in the present embodiment, the sizes of theparts of rotating shaft 9 are not limited to the above-mentioned sizes.In rotating shaft 9, the range of the length of first straight part 9 eis 1 to 3 mm, the range of the length of tapered part 9 d includingconstriction part 9 g is 0.5 to 4 mm, and the range of the length ofsecond straight part 9 f is 1.5 to 5 mm.

In addition, rear end part 9 b of rotating shaft 9 may not be providedwith knurling, and constriction part 9 h may not be formed. In thiscase, second straight part 9 f may have a length of 5 mm or greater.

Embodiment 2

Tapered part 9 d is provided in rotating shaft 9 in Embodiment 1. InEmbodiment 2, tapered part 6 d (see FIG. 4) is provided in sleeve 6.

Configuration of Electric Motor

FIG. 3 is a sectional view of an electric motor in a heat sink apparatusof Embodiment 2. The heat sink apparatus illustrated in FIG. 3 isdifferent from the heat sink apparatus illustrated in FIG. 1 in shapesof sleeve 6 and rotating shaft 9.

In the present embodiment, rotating shaft 9 is not provided with taperedpart 9 d and constriction part 9 g, and the entirety of base part 9 c isa straight part.

Shape and Dimension of Sleeve 6

Now the shape and the dimension of sleeve 6 of the present embodimentare described with reference to FIG. 4. Sleeve 6 has a cylindricalshape. Oil pool 6 a that is a circumferential groove is formed on theouter peripheral surface of sleeve 6 on the from end side, and a steppart 6 b that is a circumferential groove is formed on the outerperipheral surface of sleeve 6 on the rear end side.

In addition, tapered part 6 d having a tapered shape whose diameterincreases toward the front end side is formed at a center portion (aportion where no dynamic pressure is generated) of the inner peripheralsurface of sleeve 6. With this configuration, the inner peripheralsurface of sleeve 6 is sectioned into tapered part 6 d, first straightpart 6 e on the front end side, and second straight part 6 f on the rearend side. It is to be noted that a clearance part 6 g is formed at theconnecting portion between tapered part 6 d and first straight part 6 e.

Dynamic-pressure generation groove 6 c is formed on the outer peripheralsurfaces of first straight part 6 e and second straight part 6 f.

The sleeve 6 has a total length of 6.0 mm, an outer diameter of 4.0 mm,and an inner diameter of 1.2 mm, for example. In addition, firststraight part 6 e has a length of 1.8 mm, tapered part 6 d includingclearance part 6 g has a length of 2.0 mm, and second straight part 6 fhas a length of 2.2 mm, for example.

Effect

As described above, in the present embodiment, tapered part 6 d isformed at a center portion of sleeve 6 of the electric motor. With thisconfiguration, oil 13 can be intimately applied to a portion of rotatingshaft 9 on rotor main body 10 side by a capillary force, and it is thuspossible to achieve longer life time in comparison with a conventionalart.

In addition, as a result of a study on the capillary force, it wasconfirmed that the desirable taper angle a of tapered part 6 d is 1 to10 degrees.

In addition, it was confirmed that a similar effect is achieved also inthe case where a step part provided with multi steps whose diametersincrease toward the front end side is formed at a center portion (aportion where no dynamic pressure is generated) of sleeve 6 in place oftapered part 6 d.

It is to be noted that, in the present embodiment, the sizes of theparts of sleeve 6 are not limited to the above-mentioned sizes. Insleeve 6, the range of the length of first straight part 6 e is 1 to 3mm, the range of the length of tapered part 6 d including clearance part6 g is 0.5 to 4 mm, and the range of the length of second straight part6 f is 1.5 to 5 mm.

Embodiment 3 Configuration of Electric Motor

FIG. 5 is a sectional view of an electric motor in a heat sink apparatusof Embodiment 3. The heat sink apparatus illustrated in FIG. 5 isdifferent from the heat sink apparatus illustrated in FIG. 1 in shape ofrotating shaft 9.

In the present embodiment, neither tapered part 9 d or constriction part9 g is formed at a center portion of rotating shaft 9, and first taperedpart 9 d 1 and second tapered part 9 d 2 are formed in place of taperedpart 9 d and constriction part 9 g (see FIGS. 6A to 6F).

Shape and Dimension of Rotating Shaft 9

Now the shape and the dimension of rotating shaft 9 of the presentembodiment are described with reference to FIGS. 6A to 6F. It is to benoted that the examples of rotating shaft 9 illustrated in FIGS. 6A to6F are different in their ratios between the length of first taperedpart 9 d 1 and the length of second tapered part 9 d 2.

At a center portion (a portion where no dynamic pressure is generated)of rotating shaft 9, first tapered part 9 d 1 having a tapered shapewhose diameter decreases toward front end part 9 a side and secondtapered part 9 d 2 having a tapered shape whose diameter increasestoward front end part 9 a side are formed. With this configuration, basepart 9 c (a portion other than front end part 9 a and rear end part 9 b)of rotating shaft 9 is sectioned into first tapered part 9 d 1, secondtapered part 9 d 2, first straight part 9 e on front end part 9 a side,and second straight part 9 f on rear end part 9 b side. It is to benoted that, in view of ease of working and the like, third straight part9 d 3 may be formed at the connecting portion between first tapered part9 d 1 and second tapered part 9 d 2.

A region including first tapered part 9 d 1, second tapered part 9 d 2and third straight part 9 d 3 (hereinafter referred to as “taperedregion”) serves as an oil pool.

Rotating shaft 9 has a total length of 9 mm, and an outer diameter of1.2 mm, for example. In addition, first straight part 9 e has a lengthof 1.4 mm, the tapered region has a length of 2.2 mm, and secondstraight part 9 f has a length of 2.8 mm, for example.

Study on Capillary Force

The present inventors studied the capillary force in rotating shafts 9illustrated in FIGS. 6A to 6F. The resulting evaluations are shown inFIG. 7.

It was confirmed that in the case where first tapered part 9 d 1 islonger than second tapered part 9 d 2, that is, in the case where theratio of the length of first tapered part 9 d 1 (“B” in FIGS. 6A to 6Fand FIG. 7) to the length of second tapered part 9 d 2 (“A” in FIGS. 6Ato 6F and FIG. 7) is greater than 1 (FIGS. 6C, 6D, 6E, and 6F), thebubbles in the tapered region can be moved to front end part 9 a side,and oil 13 in the tapered region can be moved to rotor main body 10 sideof rotating shaft 9 by a capillary force (the evaluation “good” or“fair” in FIG. 7). In addition, it was confirmed that the desirabletaper angle of first tapered part 9 d 1 is 1 to 10 degrees.

Also, it was confirmed that in the case where first tapered part 9 d 1is shorter than second tapered part 9 d 2, that is, in the case wherethe ratio of the length of first tapered part 9 d 1 to the length ofsecond tapered part 9 d 2 is smaller than 1 (FIG. 6A), the bubbles inthe tapered region are moved to rotor main body 10 side and consequentlyoil 13 in the tapered region cannot be moved to rotor main body 10 side(the evaluation “poor” in FIG. 7).

Also, it was confirmed that in the case where the length of firsttapered part 9 d 1 is approximately equal to the length of secondtapered part 9 d 2 (FIG. 6B), the bubbles in the tapered region do notmove and consequently oil 13 in the tapered region cannot besufficiently moved to rotor main body 10 side (the evaluation “poor” inFIG. 7).

Effect

As described above, in the present embodiment, first tapered part 9 d 1whose diameter decreases toward front end part 9 a side and secondtapered part 9 d 2 whose diameter increases toward front end part 9 aside are formed at a center portion of rotating shaft 9 of the electricmotor such that first tapered part 9 d 1 is longer than second taperedpart 9 d 2. With this configuration, oil 13 can be intimately applied toa portion of rotating shaft 9 on rotor main body 10 side (secondstraight part 9 f) by a capillary force, and it is thus possible toachieve longer life time in comparison with a conventional art.

It is to be noted that, in the present embodiment, the sizes of theparts of rotating shaft 9 are not limited to the above-mentioned sizes.In rotating shaft 9, the range of the length of first straight part 9 eis 1.5 to 10 mm, the range of the length of tapered region is 0.5 to 4mm, and the range of the length of second straight part 9 f is 1 to 8mm.

In addition, the connecting portion between first tapered part 9 d 1 andsecond tapered part 9 d 2 may have shapes other than that of thirdstraight part 9 d 3 such as a tapered part and a constriction part.

In addition, rear end part 9 b of rotating shaft 9 may not be providedwith knurling, and constriction part 9 h may not be formed. In thiscase, first straight part 9 e may have a length of 5 mm or greater.

Embodiment 4

First tapered part 9 d 1 and second tapered part 9 d 2 are provided inrotating shaft 9 in Embodiment 3. In Embodiment 4, first tapered part 6d 1 and second tapered part 6 d 2 (see FIGS. 9A to 9F) are provided insleeve 6.

Configuration of Electric Motor

FIG. 8 is a sectional view of an electric motor in a heat sink apparatusof Embodiment 4. The heat sink apparatus illustrated in FIG. 8 isdifferent from the heat sink apparatus illustrated in FIG. 5 in shapesof sleeve 6 and rotating shaft 9.

In the present embodiment, rotating shaft 9 is provided with no taperedregion, and the entirety of base part 9 c is a straight part.

Shape and Dimension of Sleeve 6

Now the shape and the dimension of sleeve 6 of the present embodimentare described with reference to FIGS. 9A to 9F. It is to be noted thatthe examples of sleeve 6 illustrated in FIGS. 9A to 9F are different intheir ratios between the length of first tapered part 6 d 1 and thelength of second tapered part 6 d 2.

Sleeve 6 has a cylindrical shape. Oil pool 6 a that is a circumferentialgroove is formed on the outer peripheral surface of sleeve 6 on thefront end side, and step part 6 b that is a circumferential groove isformed on the outer peripheral surface of sleeve 6 on the rear end side.

In addition, first tapered part 6 d 1 having a tapered shape whosediameter increases toward the front end side and second tapered part 6 d2 having a tapered shape whose diameter decreases toward the front endside are formed at a center portion (a portion where no dynamic pressureis generated) of the inner peripheral surface of sleeve 6. With thisconfiguration, the inner peripheral surface of sleeve 6 is sectionedinto first tapered part 6 d 1, second tapered part 6 d 2, first straightpart 6 e on the front end side, and second straight part 6 f on the rearend side. It is to be noted that, in view of ease of working and thelike, third straight part 6 d 3 may be formed at the connecting portionbetween first tapered part 6 d 1 and second tapered part 6 d 2.

A region including first tapered part 6 d 1, second tapered part 6 d 2and third straight part 6 d 3 (hereinafter referred to as “taperedregion”) serves as an oil pool.

Dynamic-pressure generation groove 6 c is formed on the outer peripheralsurfaces of first straight part 6 e and second straight part 6 f.

Sleeve 6 has a total length of 6.0 mm, an outer diameter of 4.0 mm, andan inner diameter of 1.2 mm, for example. In addition, first straightpart 6 e has a length of 1.8 mm, the tapered region has a length of 2.0mm, and second straight part 6 f has a length of 2.2 mm, for example.

Study on Capillary Force

The present inventors studied the capillary force in sleeves 6illustrated in FIGS. 9A to 9F. The resulting evaluations are shown inFIG. 10.

It was confirmed that in the case where first tapered part 6 d 1 islonger than second tapered part 6 d 2, that is, in the case where theratio of the length of first tapered part 6 d 1 (“B” in FIGS. 9A to 9Fand FIG. 10) to the length of second tapered part 6 d 2 (“A” in FIGS. 9Ato 9F and FIG. 10) is greater than 1 (FIGS. 9C, 9D, 9E and 9F), thebubbles in the tapered region can be moved to the front end side, andoil 13 in the tapered region can be moved to rotor main body 10 side ofrotating shaft 9 by a capillary force (the evaluation “good” or “fair”in FIG. 10). In addition, it was confirmed that the desirable taperangle of first tapered part 6 d 1 is 1 to 10 degrees.

In addition, it was confirmed that in the case where first tapered part6 d 1 is shorter than second tapered part 6 d 2, that is, in the casewhere the ratio of the length of first tapered part 6 d 1 to the lengthof second tapered part 6 d 2 is smaller than 1 (FIG. 9A), the bubbles inthe tapered region move to rotor main body 10 side and consequently oil13 in the tapered region cannot be moved to rotor main body 10 side (theevaluation “poor” in FIG. 10).

In addition, it was confirmed that in the case where the length of firsttapered part 6 d 1 is approximately equal to the length of secondtapered part 6 d 2 (FIG. 9B), the bubbles in the tapered region do notmove and consequently oil 13 in the tapered region cannot besufficiently moved to rotor main body 10 side (the evaluation “poor” inFIG. 10).

Effect

As described above, in the present embodiment, first tapered part 6 d 1whose diameter increases toward the front end side of rotating shaft 9and second tapered part 6 d 2 whose diameter decreases toward the frontend side of rotating shaft 9 are formed at a center portion of sleeve 6of the electric motor, and first tapered part 6 d 1 is longer thansecond tapered part 6 d 2 is. With this configuration, by a capillaryforce, oil 13 can be intimately applied to a portion of rotating shaft 9on rotor main body 10 side (second straight part 9 f), and it is thuspossible to achieve longer life time in comparison with a conventionalart.

It is to be noted that, in the present embodiment, the sizes of theparts of sleeve 6 are not limited to the above-mentioned sizes. Insleeve 6, the range of the length of first straight part 6 e is 1.5 to10 mm, the range of the length of tapered region is 0.5 to 4 mm, and therange of the length of second straight part 6 f is 1 to 8 mm.

In addition, the connecting portion between first tapered part 6 d 1 andsecond tapered part 6 d 2 may have shapes other than that of thirdstraight part 6 d 3 such as a tapered part and a constriction part.

The present invention is not limited to the drawings and the embodimentsdescribed above. It should be understood by those skilled in the artthat various modifications, combinations, sub-combinations andalterations may occur depending on design requirements and other factorsin so far as they are within the scope of the appended claims or theequivalents thereof.

While the electric motor is used for a heat sink apparatus in theembodiments, the present invention is not limited to this, and theelectric motor may also be used for other apparatuses such as an exhaustfan.

An electric motor according to a mode of the present disclosureincludes: a frame including a frame housing having a cylindrical shapewhose one end is open; a sleeve fitted in the frame housing; a statorattached to an outer peripheral part of the frame housing; and a rotorincluding a rotating shaft rotatably and pivotally supported by thesleeve, and a magnet that is disposed opposite to the stator, one end ofthe rotating shaft being fixed. The rotating shaft has a columnar shape.A tapered part having a tapered shape whose diameter decreases toward aside of a front end of the rotating shaft is formed in a center portionof the rotating shaft, the front end being a free end. A length of thetapered part is greater than a diameter of the rotating shaft. Oil isprovided to a gap between the rotating shaft and the sleeve.

In the electric motor above, the tapered part has a taper angle of 1 to3 degrees.

In the electric motor above, the tapered part is sandwiched between twostraight parts, each of the two straight parts having a constantdiameter.

In the electric motor above, a second tapered part having a taperedshape whose diameter decreases toward a side of a fixed end of therotating shaft is formed in the center portion of the rotating shaft,the second tapered part being formed to extend from a first straightpart that is one of the two straight parts on the free end side. Thetapered part is formed to extend from a second straight part that isanother of the two straight parts on the fixed end side. A length of thetapered part is greater than a length of the second tapered part. Ataper angle of the tapered part is smaller than a taper angle of thesecond tapered part.

An electric motor according to a mode of the present disclosureincludes: a frame including a frame housing having a cylindrical shapewhose one end is open; a sleeve fitted in the frame housing; a statorattached to an outer peripheral part of the frame housing; and a rotorincluding a rotating shaft rotatably and pivotally supported by thesleeve, and a magnet that is disposed opposite to the stator, one end ofthe rotating shaft being fixed. The rotating shaft has a columnar shape.A step part provided with a plurality of steps whose diameters decreasetoward a side of a front end of the rotating shaft is formed in a centerportion of the rotating shaft, the front end being a free end. A lengthof the step part is greater than a diameter of the rotating shaft. Oilis provided to a gap between the rotating shaft and the sleeve.

In the electric motor above, the step part is sandwiched between twostraight parts, each of the two straight parts having a constantdiameter.

In the electric motor above, a dynamic-pressure generation groove thatholds the oil is formed in at least one of an outer peripheral surfaceof the rotating shaft and an inner peripheral surface of the sleeve.

A heat sink apparatus according to a mode of the present disclosure is acooling fan motor including the electric motor above. A heat generationmember is attachable to the frame of the electric motor.

In the electric motor above, a second tapered part having a taperedshape whose diameter increases toward the free end side is formed in thecenter portion of the rotating shaft. A length of the tapered part isgreater than a length of the second tapered part.

In the electric motor above, a taper angle of the tapered part is 1 to10 degrees.

In the electric motor above, a sum of the length of the tapered part andthe length of the second tapered part is greater than a diameter of therotating shaft.

A heat sink apparatus according to a mode of the present disclosure is acooling fan motor including the electric motor above. A heat generationmember is attachable to the frame of the electric motor.

INDUSTRIAL APPLICABILITY

The present invention is suitable for an electric motor and a heat sinkapparatus using the same.

REVERENCE SIGNS LIST

1 Frame

1 a Frame housing

3 Stator

5 Thrustor

6 Sleeve

6 c Dynamic-pressure generation groove

6 d Tapered part

6 d 1 First tapered part

6 d 2 Second tapered part

6 d 3 Third straight part

6 e First straight part

6 f Second straight part

7 Fixation ring

8 Fan

9 Rotating shaft

9 a Front end part

9 b Rear end part

9 c Base part

9 d Tapered part

9 d 1 First tapered part

9 d 2 Second tapered part

9 d 3 Third straight part

9 e First straight part

9 f Second straight part

9 g Constriction part

10 Rotor main body

11 Magnet

12 Magnet yoke

13 Oil

1. An electric motor comprising: a frame including a frame housinghaving a cylindrical shape whose one end is open; a sleeve fitted in theframe housing; a stator attached to an outer peripheral part of theframe housing; and a rotor including a rotating shaft rotatably andpivotally supported by the sleeve, and a magnet that is disposedopposite to the stator, one end of the rotating shaft being fixed,wherein: the rotating shaft has a columnar shape; a tapered part havinga tapered shape whose diameter decreases toward a side of a front end ofthe rotating shaft is formed in a center portion of the rotating shaft,the front end being a free end; a length of the tapered part is greaterthan a diameter of the rotating shaft; and oil is provided to a gapbetween the rotating shaft and the sleeve.
 2. The electric motoraccording to claim 1, wherein the tapered part has a taper angle of 1 to3 degrees.
 3. The electric motor according to claim 1, wherein thetapered part is sandwiched between two straight parts, each of the twostraight parts having a constant diameter.
 4. The electric motoraccording to claim 3, wherein: a second tapered part having a taperedshape whose diameter decreases toward a side of a fixed end of therotating shaft is formed in the center portion of the rotating shaft,the second tapered part being formed to extend from a first straightpart that is one of the two straight parts on the free end side; thetapered part is formed to extend from a second straight part that isanother of the two straight parts on the fixed end side; a length of thetapered part is greater than a length of the second tapered part; and ataper angle of the tapered part is smaller than a taper angle of thesecond tapered part.
 5. An electric motor comprising: a frame includinga frame housing having a cylindrical shape whose one end is open; asleeve fitted in the frame housing; a stator attached to an outerperipheral part of the frame housing; and a rotor including a rotatingshaft rotatably and pivotally supported by the sleeve, and a magnet thatis disposed opposite to the stator, one end of the rotating shaft beingfixed, wherein: the rotating shaft has a columnar shape; a step partprovided with a plurality of steps whose diameters decrease toward aside of a front end of the rotating shaft is formed in a center portionof the rotating shaft, the front end being a free end; a length of thestep part is greater than a diameter of the rotating shaft; and oil isprovided to a gap between the rotating shaft and the sleeve.
 6. Theelectric motor according to claim 5, wherein the step part is sandwichedbetween two straight parts, each of the two straight parts having aconstant diameter.
 7. The electric motor according to claim 1, wherein adynamic-pressure generation groove that holds the oil is formed in atleast one of an outer peripheral surface of the rotating shaft and aninner peripheral surface of the sleeve.
 8. A heat sink apparatus that isa cooling fan motor including the electric motor according to claim 1,wherein a heat generation member is attachable to the frame of theelectric motor.